1. Field of the Invention
The present invention relates to a magnetic bubble file system, and more particularly to a magnetic bubble file system having a write protection function.
2. Description of the Prior Art
In a storage device such as a magnetic disk, each record unit is divided into an Identification (ID) field and a data field, and when the record unit is to be read or written, the ID field may be read or written before the data field is read or written, because, in the storage device such as the magnetic disk, a read/write unit, that is, a bit length can be more or less flexibly determined. Thus, in the magnetic disk, a write protection information may be stored in the ID field of each record unit so that write enable or write disable status can be determined in accordance with the information in the ID field.
On the other hand, in a magnetic bubble memory, a record unit is a page and a whole page must be read or written because of the complexity of control for magnetic bubble memory devices. It is very difficult to switch the read and write operations in one access to one page. Accordingly, it is not possible to store write protect information with the data in each page and read out the write protect information when the page is to be accessed in order to determine whether information can be written or not. Accordingly, the write protection function for each record unit is not attained, as opposed to the magnetic disk.
Japanese Patent Application Laid-Open Publication No. 65390/81 discloses a magnetic bubble memory control system for controlling a bubble memory in which read control information is updated based on a specific condition of information read from the magnetic bubble memory so that a file storage device is provided with a simple configuration. However, it does not teach the write protection.
An article "method for operating Hitachi IM-bit magnetic memory board" Hitachi Electronic Components Technical Data, July 1, 1982 discloses a system in which defect loop information is stored in a magnetic bubble memory and it is read out at a first access to the bubble and stored in a RAM, and in subsequent accesses, the stored information is referenced so that read and write operations are carried out for valid loops. However, it does not teach the write protection function for each page.